1. Field of the Invention
The present invention relates to photovoltaic elements with excellent weatherability and durability.
2. Description of Related Art
With growing awareness of environmental issues, research and development has been brisk on solar cells and, in addition to the conventional ground installation type and roof installation type solar cells, building-material-integrated solar cell modules have also been developed heretofore in structure in which a photovoltaic element was integrated with a building material and which was provided with both a power generating function as a solar cell and a satisfactory design as a roof material.
On the other hand, attempts are being made to implement utilization of solar cell modules as a small-scale power plant in which the solar cell modules tailored to only the power generating function are installed under a managed environment, for the pursuit of reduction of power generation cost. The managed environment is a perfectly managed circumstance in which the solar cell modules installed are surrounded with fences or walls and locked away, so as to allow no other ordinary people than responsible people to enter the inside. The solar cell modules installed under such a managed environment have the potential for reducing the power generation cost on the basis of relaxing part of safety designs resistant to all accidental events that the conventional general-purpose solar cell modules took into consideration. For example, the conventional solar cell modules were designed with a covering configuration enough to retain sufficient insulation even in the event that a person untrained for handling happens to scratch the surface to make surface scars. The solar cell modules installed under the managed environment do not have to take such an event into consideration, so that the covering material can be reduced greatly.
The present inventors suggested, as a proposal of such solar cell modules, a photovoltaic element in which a power generating area was provided with a thin film resin layer having a minimum covering configuration enough to prevent the photovoltaic element from directly contacting water such as rain or the like. There is a possibility of providing an exceptionally inexpensive photovoltaic power system in structure in which such photovoltaic elements are installed under the managed environment.
FIGS. 4A and 4B are schematic illustrations showing an example of the photovoltaic element as described above, wherein FIG. 4A is a front view and FIG. 4B a sectional view taken along line 4Bxe2x80x944B of FIG. 4A. In FIGS. 4A and 4B, reference numeral 401 designates an electroconductive substrate, 402 a back reflecting layer, 403 a photoelectric conversion layer, 404 a transparent electrode, 404b a transparent-electrode-layer-removed portion, 405a a grid electrode, 405b a positive bus-bar electrode, 406 an insulating member, and 407 a thin film resin layer.
The bus-bar electrode 405b is usually made of metal foil, specifically, foil of silver, copper, or the like.
The insulating member 406 is normally of structure in which adhesive members are laid on both surfaces of a polymer film. This insulating member 406 functions to retain electrical insulation between the bus-bar electrode 405b and the conductive substrate 401 and also functions as a spacer for preventing a short of the photovoltaic element due to a burr of the bus-bar electrode 405b or the like. The polymer film making up the insulating member 406 usually has a thickness of approximately 100 xcexcm. The adhesive members used in this insulating member 406 are selected from a variety of adhesive materials. When the photovoltaic element is constructed in the minimum covering configuration, the adhesive material itself needs to have weatherability and is thus selected, for example, from silicone adhesive materials or the like. In addition, the adhesive members need to have a thickness of not less than 30 xcexcm in order to ensure good adhesion to the photovoltaic element and the bus-bar electrode 405b. 
However, in order to substantiate practical use of the above-described photovoltaic element having only the thin film resin layer 407 as a covering member, there are the following fears.
The thin film resin layer 407 has to be an inexpensive, simple covering that also provides the photovoltaic element with satisfactory weatherability. Conventionally, this thin film resin layer 407 was a simple covering mainly comprised of EVA (ethylene-vinyl acetate copolymer), and conceivable covering methods in this case include a laminating method of laminating a sheet form of EVA by well-known laminating apparatus and a method of applying molten EVA onto the photovoltaic element by casting.
However, the laminating method has the problem of high instrument cost, while the casting method has the problem that it is hard to cover an uneven photovoltaic element having collecting electrodes and others formed on its light-receiving surface, with molten EVA having a very high viscosity.
Further, because surfaces of EVA are easy to soil, a film or glass for preventing contamination is essential, which makes reduction of material cost difficult. Moreover, the material has a low adhesion to the adhesive material of the aforementioned insulating member 406 and is easily subject to peeling off in the outdoor environment. It will allow water to intrude through an interface between the covering member and the adhesive member, thereby inducing deterioration of the transparent electrode layer 404 or deterioration at various interfaces in the photovoltaic element, which may result in peeling off or the like that greatly degrades the electrical characteristics.
A conventional solution to the above problem was a method of providing a glass or ETFE film as a surface member, further increasing the thickness of the covering member of EVA or the like, and covering the entire photovoltaic element, and it cannot be a method capable of achieving the cost reduction which is required for the photovoltaic element.
In view of the above problems, it is an object of the present invention to provide photovoltaic elements with excellent characteristics of weatherability and durability on the basis of a simple covering configuration capable of achieving cost reduction.
A specific feature of the present invention achieving the above object is as follows.
Namely, an aspect of the present invention is a photovoltaic element comprising a first collecting electrode and a second collecting electrode on a light-receiving surface and having a configuration such that the first and the second collecting electrodes are electrically joined to each other on an insulating member, wherein a first resin layer is provided on at least a portion of the light-receiving surface, and wherein a boundary between the first resin layer and the insulating member is covered by a second resin layer having a high compatibility with a component of the insulating member.
Preferably, the second resin layer and the component of the insulating member are a polymer comprised of a monomer comprising at least one siloxane.
Preferably, the insulating member is comprised of a laminate of an insulating film and an adhesive member and the second resin layer has a high compatibility with the adhesive member.
Preferably, the second resin layer and the adhesive member are a polymer comprised of a monomer comprising at least one siloxane.
Preferably, the first resin layer is a polymer comprised of a monomer comprising at least one vinyl group.
Preferably, the second resin layer is a polymer comprised of a monomer comprising at least one vinyl group.
The photovoltaic element of the present invention described above may further include any of the following preferred features:
xe2x80x9cthe second resin layer fills in a portion of a gap which the adhesive member has;xe2x80x9d
xe2x80x9cthe second resin layer is comprised of a material having a viscosity of 300-2000 mPaxc2x7s;xe2x80x9d
xe2x80x9cthe second resin layer covers at least a power-generating-region-side section of the second collecting electrode;xe2x80x9d
xe2x80x9cthe second resin layer covers a connection between the first and the second collecting electrodes;xe2x80x9d
xe2x80x9cthe second resin layer covers the top of the second collecting electrode;xe2x80x9d
xe2x80x9cthe first resin layer contains an ultraviolet absorber and a concentration of the ultraviolet absorber has a depth profile in a direction from a light-receiving surface side toward a non-light-receiving surface side.xe2x80x9d
Another photovoltaic element of the present invention is a photovoltaic element comprising:
a substrate having a photovoltaic layer on a light-receiving surface side thereof;
a first collecting electrode provided on the light-receiving surface side of the substrate, for collecting electricity generated in the photovoltaic layer;
a first resin layer covering a light-receiving surface of the substrate;
an insulating member provided in a portion between the photovoltaic layer and the first collecting electrode so as to be in contact with the first resin layer, for establishing electrical insulation at a portion between the photovoltaic layer and the first collecting electrode; and
a second resin layer covering at least a boundary between the first resin layer and the insulating member and having a high compatibility with the insulating member.
Preferably, the insulating member is comprised of a laminate of an insulating film and an adhesive member and the second resin layer has a high compatibility with the adhesive member.
Still another photovoltaic element of the present invention is a photovoltaic element comprising:
a substrate having a photovoltaic layer on a light-receiving surface side thereof;
a first collecting electrode provided on the light-receiving surface side of the substrate, for collecting electricity generated in the photovoltaic layer;
a first resin layer covering a light-receiving surface of the substrate;
an insulating member provided in a portion between the photovoltaic layer and the first collecting electrode so as to be in contact with the first resin layer, for establishing electrical insulation at a portion between the photovoltaic layer and the first collecting electrode; and
a second resin layer covering at least a boundary between the first resin layer and the insulating member,
wherein the second resin layer and the insulating member are a polymer comprised of a monomer comprising at least one siloxane.
Preferably, the insulating member is comprised of a laminate of an insulating film and an adhesive member and the adhesive member is a polymer comprised of a monomer comprising at least one siloxane.